A trough-type scraper conveyor has a chain that extends and is advanced longitudinally in a trough to move large particulate material such as ore or coal longitudinally in the trough. To this end the chain has a succession of links, with so-called coupling links alternating with entrainment links and entrainment devices such as scrapers, plates, or even buckets are attached to the entrainment links. The coupling links merely serve to transmit longitudinal force along the normally tensioned chain.
The links of a standard such chain are simple longitudinally extending link plates interconnected by transverse pivot pins that extend through bores at the ends of the link plates. The pins each have one end formed with a head and an opposite end formed with a transversely throughgoing passage through which a cotter pin or the like extends to prevent the respective pin from moving along its own axis transverse to the respective link plates relative to the chain. The entrainment elements in turn are bolted or welded to the sides of the entrainment links between the respective pins. Such an arrangement therefore has quite a few parts and is burdensome to assembly, particularly when making repairs in the field.
In addition it is possible, as seen in German Patent document No. 2,416,289 based on an application filed Apr. 4, 1973 in Italy by G. DiRosa, to form one of the plates of the entrainment link with a tab constituting an entrainment element. In this system the pivot pins have T-heads which can be engaged in transverse grooves of the entrainment links. Such a system is fairly handy, but requires meticulously cast and/or machined link plates that are expensive to fabricate. What is more when the chain is slack it is possible for the pins to move into a position in which they can come loose from the respective links.
It is known from other types of chains to provide specially made link pins which can be installed without the use of further parts, and which are fairly secure once in place. For instance German Patent No. 898,878 based on patent applications filed in Britian Sept. 29, 1948 and Sept. 15, 1949 by D. M. King discloses an arrangement wherein link has two parts, a U-shaped element whose legs have rounded ends and which are formed with respective aligned keyhole-shaped holes, and a pin having a diameter equal to that of the round part of the respective hole and two pairs of grooves allowing it to slide into the straight and narrow part of the respective hole. The aligned keyholes are spaced in from the free ends of the respective legs and the bights interconnecting these legs are so constructed that they can only be positioned to surround the respective keyhole round part when perpendicular to the respective link plate. The pin can then be fitted through the hole and then slid back with the other link to move into the narrow section and allow the two links to move into longitudinal allignment. So long as such a chain remains fairly straight, the pin cannot fall out. Such an arrangement is not usable in a conveyor chain which occasionally jams from overloading so that a portion of the chain downstream of the overload can be left completely slack and even bent over itself, as in this position the pivot pins could fall out and allow the chain to open up.
U.S. Pat. No. 3,021,718 also of D. M. King suggests a solution to this problem in a chain whose every other link is formed by a a pair of adjacent closed and longitudinally elongated loops into whose ends a longitudinal brace forces the pivot pins. Presumably the brace exerts continuous longitudinal pressure keep the pins in place. Obviously such a system could not stand the shocks and rough treatment of use in a conveyor chain, where the pins could be counted on to fall out in short order.